In this paper, a new ultra-local model control approach is proposed. The concept is based on the linear adaptive observer to estimate the ultra-local model parameters instead of algebraic derivation technique. The importance of adaptive observer is deduced in the join estimation of state and unknown parameters of parametric systems. The closedloop control is implemented via an adaptive PID controller to reject disturbances due to exogenous parameter uncertainties. In this paper, a performance

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... mparison between the adaptive observer based method and the algebraic derivation technique is developed to show the efficiency of the proposed control strategy. The approaches are applied to a two-tank system for the water level control. Several successful simulation results are shown to demonstrate the effectiveness of the proposed controller.